Dissociation constants, table

Because of the scarcity of electronic paramagnetic resonance data, and because of the frequent unreliability of the data from paramagnetism, boiling point elevation, spectrophotometry, and ortho-para hydrogen conversion, most published radical dissociation constants can be accepted only with reservations. An error of 50 % is not at all improbable in many cases. We are therefore not yet in a position to explain, or rather to test our explanations of, small differences in dissociation constants. Table I shows the values of K corresponding to various hexaarylethanes in benzene at 25°. Because of the order of magnitude differences in Table I, however, it is likely that some of the expected large effects, such as steric and resonance effects, exist. 

The dioxo complexes of W(IV) and Mo(IV), having high pKa values (Table II), are formed via hydrolysis as the rate-determining step (Scheme 4) and the observed rate constants for the inversion along the O-M-O axis for the W(IV) and the Mo(IV) complexes are therefore defined by Eq. (18). These were calculated as a function of pH, using the proton exchange rate constants (Table IV) and the acid dissociation constants (Table II)... 

Because the forward reaction is endergonic, increased temperature drives the system to products, increasing the value for the water dissociation constant. Table 16.2 shows values for this reaction at different temperatures. 

These values were calculated from those for iti or ibi and the dissociation constants (Table IV). 

The formation of complexes has a strong influence on metal dissolution. Some anions form strong complexes with very small values of their dissociation constants. Table 1.8 gives some examples. Au forms very stable complexes according to Equation 1.154a with the related equilibrium constant of Equation 1.154b. 

Dissociation Constants for Selected Br0nsted Acids (Table 4 2, p 135)... 

Table 1 6 VSEPR and Molecular Geometry Table 1 7 Dissociation Constants (pK ) of Acids Table 2 5 Oxidation Numbers in Compounds with More Than One Carbon...

The values listed in Tables 8.7 and 8.8 are the negative (decadic) logarithms of the acidic dissociation constant, i.e., — logj, For the general proton-transfer reaction... 

This table lists the and pi (pH at the isoelectric point) values of a-amino acids commonly found in proteins along with their abbreviations. The dissociation constants refer to aqueous solutions at 25°C. 

The physical properties of cyanoacetic acid [372-09-8] and two of its ester derivatives are Hsted ia Table 11 (82). The parent acid is a strong organic acid with a dissociation constant at 25°C of 3.36 x 10. It is prepared by the reaction of chloroacetic acid with sodium cyanide. It is hygroscopic and highly soluble ia alcohols and diethyl ether but iasoluble ia both aromatic and aUphatic hydrocarbons. It undergoes typical nitrile and acid reactions but the presence of the nitrile and the carboxyUc acid on the same carbon cause the hydrogens on C-2 to be readily replaced. The resulting malonic acid derivative decarboxylates to a substituted acrylonitrile ... 

Acrylic acid is a moderately strong carboxylic acid. Its dissociation constant is 5.5 x 10. Vapor pressure as a function of temperature is given in Table 4 for acrylic acid and four important esters (4,16—18). The lower esters form a2eotropes both with water and with their corresponding alcohols. 

Mahc acid is a relatively strong acid. Its dissociation constants are given in Table 1. The pH of a 0.001% aqueous solution is 3.80, that of 0.1% solution is 2.80, and that of a 1.0% solution is 2.34. Many of its physical properties are similar to those of citric acid (qv). Solubihty characteristics are shown in Figure 1 and Table 1, densities of aqueous solutions are hsted in Table 2, and pH values vs concentration are shown in Figure 2. 

Thiomahc acid [70-49-5] (mercaptosuccinic acid), C H O S, mol wt = 150.2, is a sulfur analogue of malic acid. The properties of the crystalline, soHd thiomalic acids ate given in Table 6. The racemic acid has the following acid dissociation constants at 25°C pTf i — 3.30 pffc2 — 4.94. 

Because iCg values for competitive antagonists represent tme dissociation constants, these make possible quantitative interpretations of SARs. Significant use also has been made of iCg values in the quantitative comparison of receptors to determine whether receptors that respond to the same agonists are identical or whether responses produced by different agonists are initiated at the same receptors (44,46). Thus, beta-adrenoceptors in human and guinea pig preparations can be direcdy compared and selective and antagonists quantitated (Table 3). 

Table 3. Equilibrium Dissociation Constants for Drug—Receptor Complexes In Vitro...

DMAMP and AMP are among the strongest amines commercially available. The dissociation constants of these materials appear in Table 2. AH alkan olamines have slight amine odors in the Hquid state the soHds are nearly odorless. 

Physical properties of the acid and its anhydride are summarized in Table 1. Other references for more data on specific physical properties of succinic acid are as follows solubiUty in water at 278.15—338.15 K (12) water-enhanced solubiUty in organic solvents (13) dissociation constants in water—acetone (10 vol %) at 30—60°C (14), water—methanol mixtures (10—50 vol %) at 25°C (15,16), water—dioxane mixtures (10—50 vol %) at 25°C (15), and water—dioxane—methanol mixtures at 25°C (17) nucleation and crystal growth (18—20) calculation of the enthalpy of formation using semiempitical methods (21) enthalpy of solution (22,23) and enthalpy of dilution (23). For succinic anhydride, the enthalpies of combustion and sublimation have been reported (24). 

Table 10. Dissociation Constant for Straight-Chain and Chlorinated Alkanoic Acids at 25°C ...

The acid dissociation constants of some representative carboxylic acids are tabulated in Table 4. 

Theoretical and structural studies have been briefly reviewed as late as 1979 (79AHC(25)147) (discussed were the aromaticity, basicity, thermodynamic properties, molecular dimensions and tautomeric properties ) and also in the early 1960s (63ahC(2)365, 62hC(17)1, p. 117). Significant new data have not been added but refinements in the data have been recorded. Tables on electron density, density, refractive indexes, molar refractivity, surface data and dissociation constants of isoxazole and its derivatives have been compiled (62HC(17)l,p. 177). Short reviews on all aspects of the physical properties as applied to isoxazoles have appeared in the series Physical Methods in Heterocyclic Chemistry (1963-1976, vols. 1-6). 

A very interesting steric effect is shown by the data in Table 7-12 on the rate of acid-catalyzed esterification of aliphatic carboxylic acids. The dissociation constants of these acids are all of the order 1(T, the small variations presumably being caused by minor differences in polar effects. The variations in esterification rates for these acids are quite large, however, so that polar effects are not responsible. Steric effects are, therefore, implicated indeed, this argument and these data were used to obtain the Es steric constants. Newman has drawn attention to the conformational role of the acyl group in limiting access to the carboxyl carbon. He represents maximum steric hindrance to attack as arising from a coiled conformation, shown for M-butyric acid in 5. 

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